SAM4CP [DATASHEET]
43051E–ATPL–08/14
26
6.
Input/Output Lines
The SAM4CP has two types of input/output (I/O) lines: general purpose I/Os (GPIO) and system I/Os. GPIOs have
alternate functionality due to multiplexing capabilities of the PIO controllers. The same PIO line can be used whether in
I/O mode or by the multiplexed peripheral. System I/Os include pins such as test pins, oscillators, erase or analog inputs.
6.1
General Purpose I/O Lines
GPIO lines are managed by PIO Controllers. All I/Os have several input or output modes such as pull-up or pull-down,
input Schmitt triggers, multi-drive (open-drain), glitch filters, debouncing or input change interrupt. Programming of these
modes is performed independently for each I/O line through the PIO controller user interface. For more details, refer to
the “Parallel Input/Output (PIO) Controller” section of this datasheet.
The input/output buffers of the PIO lines are supplied through VDDIO power supply rail when used as general purpose
IOs (GPIOs). When used as extra functions like LCD or analog modes, GPIO lines have either VDDLCD or VDDIN
voltage range.
Each I/O line embeds an ODT (On-die Termination) shown in
Figure 6-1
below. ODT consists of an internal series
resistor termination scheme for impedance matching between the driver output (SAM4CP) and the PCB trace impedance
preventing signal reflection. The series resistor helps to reduce IOs switching current (di/dt) thereby reducing EMI. It also
decreases overshoot and undershoot (ringing) due to inductance of interconnect between devices or between boards.
Finally, ODT helps diminish signal integrity issues.
Figure 6-1.
On-die Termination
6.2
System I/O Lines
System I/O lines are pins used by oscillators, test mode, reset and JTAG, to name but a few. Described below in
Table 6-
1
are the SAM4CP system I/O lines shared with PIO lines.
These pins are software configurable as general purpose I/O or system pins. At start-up, the default function of these
pins is always used.
Notes: 1.
If PC9 is used as PIO input in user applications, a low level must be ensured at start-up to prevent Flash
erase before the user application sets PC9 into PIO mode.
Refer to the section “3 to 20 MHz Crystal Oscillator”.
2.
PCB Trace
Z0 ~ 50 Ohms
Receiver
SAM4 Driver with
Zout ~ 10 Ohms
Rodt
Z0 ~ Zout + Rodt
ODT
36 Ohms Typ.
Table 6-1.
System I/O Configuration Pin List
SYSTEM_IO
Bit Number
Default Function
after Reset
Other
Function
Constraints
for Normal Start
Configuration
0
TDI
PB0
-
In Matrix User Interface Registers
(Refer to the System I/O
Configuration Register in the “Bus
Matrix” section of this datasheet)
1
TDO/TRACESWO
PB1
-
2
TMS/SWDIO
PB2
-
3
TCK/SWCLK
PB3
-
4
ERASE
PC9
Low level at Start-up
(1)
-
PA31
XIN
-
(2)
-
PA30
XOUT
-